> ## Documentation Index > Fetch the complete documentation index at: https://docs.symmetry.com/llms.txt > Use this file to discover all available pages before exploring further. # Form determination > How Symmetry Payroll Forms turns an employee's home and work addresses into the set of federal, state, and local withholding forms they need to complete. Form determination is the core function of SPF: you provide the employee's home and work locations, and SPF returns the withholding forms they're required to complete. The rest of an SPF integration builds on that result. ## What you supply Determination takes one **home address** and between one and ten **work addresses**. Those addresses do the heavy lifting; most of what SPF needs to know is derived from them. Three optional inputs adjust the outcome: * **[Nexus](/spf/references/multi-state-scenarios#determination-of-nexus)**: the states where your company has a business presence and is therefore subject to withholding obligations. Nexus is always assumed in a work state. For a resident state where the employee doesn't work, you have to tell SPF. If you say nothing, SPF assumes nexus exists in the resident state. * **Lock-in letters**: jurisdictions where the IRS has directed the employer to withhold at a specified minimum. A lock-in letter changes which forms and which paths the employee is offered. * **[Interstate employee](/spf/configuration/interstate-employees)**: a flag that fine-tunes outcomes for employees whose home and work states differ, mainly affecting whether certain Colorado and Oregon forms come back as recommended rather than optional. ## From address to jurisdiction An address isn't a jurisdiction. Turning one into the other is a real step, and for U.S. addresses it's handled by the Symmetry Location Service. **This section is U.S.-only.** The Symmetry Location Service does not cover Canada, so Canadian addresses are not resolved to jurisdictions this way. Location data comes back empty for Canadian locations, and nexus and lock-in letters don't apply. Canadian determination is handled by a separate processor. See the [Canadian SPF API overview](/spf/api/canadian-overview). The address is compared against USPS data and standardized, so `123 main st` and `123 Main Street` resolve identically. The normalized address is converted to latitude and longitude coordinates. Taxing jurisdiction shapefile boundaries are overlaid against those coordinates to determine which jurisdictions the location falls within: state, county, city, municipality, and school district. SPF gets back the jurisdictions that apply, plus jurisdiction-specific data that some forms need to complete themselves. That last point is easy to miss. Determination doesn't only decide *which* forms apply; it also supplies data those forms need. Pennsylvania forms require the PSD code and EIT rate for the address. Ohio forms need the school district. Indiana needs the county. All of it comes out of this step. Address normalization can also surface differences between what you submitted and what SPF resolved. See [Address result codes](/spf/references/address-result-codes) for how to interpret those, and [Address suggestions](/spf/configuration/address-suggestions) for how to present corrections to employees. ## What comes back Once jurisdictions are resolved, SPF assembles the form set. In broad terms: * The **federal** form is in scope by default. You can remove federal forms entirely (and the Federal section of Guided Mode along with them) by setting `disableFederal` to `true` in `settings.json`, in the SPF Registration JSON, or through the Admin Panel. * The **work state's** form applies, unless a reciprocal agreement removes the obligation and replaces it with an exemption certificate. * The **resident state's** form applies when it differs from the work state and that state taxes the wages. * **Local forms** are added when the specific city, municipality, or school district imposes its own withholding. Four things most often change this baseline: **Reciprocity.** When two states have a reciprocal agreement, an employee living in one and working in the other can ask to be exempt from work-state withholding and be taxed at home instead. SPF handles this by swapping the standard work-state form for that state's reciprocal exemption certificate. **Nexus.** Without a business presence in the employee's resident state, there may be no obligation to withhold there, which removes that state's form from the set. **Whether the resident state taxes out-of-state wages.** Some states tax them always, some only when the work state doesn't withhold, and some not at all. **Local jurisdictions.** Four states (Arkansas, Michigan, Oregon, and Pennsylvania) have cities and districts that publish their own withholding forms. Whether one applies depends on the specific municipality, not just the state, which is why a physical work address matters so much. The [Multi-state scenarios](/spf/references/multi-state-scenarios) reference has the full per-state table showing which states tax nonresidents, which tax out-of-state wages, and which reciprocal agreements exist. ## Recommended and optional forms Not every returned form is mandatory. Each one is marked as recommended or optional. **Recommended** forms are the ones the employee should complete based on their situation. **Optional** forms are legitimately available to them but not required: an Oregon transit tax opt-in, for example, or Colorado's DR 1059, the Affidavit of Exemption for the Nonresident Spouse of a U.S. Servicemember. How you present that distinction is up to you, and it interacts with the mode you've chosen. Guided Mode narrows the set through targeted questions; Choose Mode presents the forms and lets the employee decide. See [Form modes](/spf/core-concepts/form-modes). ## Two ways to ask SPF exposes determination through two paths, and which one you use depends on the experience you're building. Returns the forms that apply, straight from the addresses. Best when you're presenting a list for the employee to work through, or when you already know what you need. Returns one flow per applicable jurisdiction. Some flows resolve to forms immediately; others ask the employee a few questions first (about military spouse status, exemptions, or language preference) to narrow down which form in that jurisdiction is the right one. The important thing to understand about guided flows is that their questions are a *different kind of question* from the ones inside a form. Flow questions decide which forms you need. Form questions fill a form out. See [Question sets and navigation](/spf/core-concepts/question-sets-and-navigation) for how the two relate. ## Related Per-state reference for nexus, reciprocity, and nonresident taxation. What the interstate employee flag changes. The local forms SPF supports and the states that require them. The address normalization and geocoding service behind determination.